Washing machines are classified into a drum type, an agitator type and a pulsator type according to a washing method. Specifically, the drum washing machine has a protrusion portion formed on an inner wall of the cylinder. A washing operation is performed by an impact force occurring when a laundry is lifted up and dropped down along an inner circumferential surface of the drum due to the protrusion portion during a rotation of the drum.
Recently, the drum washing machine is widely used since a laundry is less damaged and a small amount of washing water is used.
FIG. 1 is a schematic view of a general drum washing machine.
Referring to FIG. 1, the drum washing machine includes a case 3 having a hollow cuboid shape, a tub 1 accommodated in the case 3 to contain water, a drum 2 formed inside the tub 1 to receive a laundry, and a driving motor 10 installed in a back of the tub 1 to rotate the drum 2.
Herein, an operation of the general drum washing machine will be described below.
First, a torque of the driving motor 10 is transferred to the drum 2 through a belt 11. If the drum 2 rotates, the laundry loaded into the drum 2 rotates together. At this time, the drum 2 rotates at a low speed. Therefore, if the laundry is placed in an upper portion of the drum during a rotation of the drum, the laundry is dropped down due to the gravity, so that the laundry collides with the washing water contained in the tub 1. The laundry stained with dirt can be washed due to the impact force occurring between the laundry and the washing water.
Additionally, the washing machine includes a weight pendulum 4 formed on one side of an outer circumference of the tub 1 to correct the center of gravity in back and forth/right and left directions of the tub 1, a spring 5 connected between the case 3 and the tub 1 to relieve an amount of vibration occurring in the tub 1 and the drum 2, and a damper 8 connected between the case 3 and the tub 1 to attenuate an amount of vibration occurring in the tub 1.
The weight pendulum 4 fundamentally eliminates the vibration due to an eccentric center of gravity of the tub 1 by matching the center of gravity of the tub 1.
Further, an amount of vibration due to the operation of the tub 1 is relieved by the spring 5 and attenuated by the damper, thereby rapidly attenuating an amount of vibration occurring during the operation of the tub 1.
In more detail, the damper 8 includes a cylinder 6 having one end portion connected to the tub 1, and a piston load 7 having one end portion connected to the case 3 and inserted into the cylinder 6.
FIG. 2 is a sectional view of a general damper.
Referring to FIG. 2, the general damper 8 includes the cylinder 6 and the piston load 7 having some portion inserted into the cylinder 6. The general damper 8 further includes a tub fixing opening 61 for allowing the piston load 7 to be connected to the tub 1, a case fixing opening 71 for allowing some portion of the piston load 7 to be connected to the case 3, a friction member 9 formed on one end portion of the piston load 7 to perform a friction action with an inner circumferential surface of the cylinder 6, and a vent 72 formed inside the piston load 7 to prevent an internal air of the cylinder 6 from being compressed.
Herein, an operation of the damper 8 will be described with reference to the structure of the damper 8.
When a predetermined amount of vibration occurs in the tub 1 and/or the drum 2, a relatively different displacement occurs in an inner circumferential surface of the cylinder 6 and an outer circumferential surface of the piston load 7. The vibration is converted into a frictional heat due to the friction member 9 formed between the cylinder 6 and the piston load 7. As a result, a frictional force of the tub 1 and/or the drum 2 is converted into a heat of the friction member 9 and then attenuated.
Additionally, in order to prevent the damper 8 from being damaged when the tub 1 is shaken in back and front/right and left directions, predetermined hole (e.g., circular hole) is formed in the tub fixing opening 61 and the case fixing opening 71, so that the damper 8 is fixed to the tub 1 and the case 3 in a freely movable state. In order to prevent the damping force from being lowered due to a compression of an internal air of the cylinder 6 when the piston load 7 moves in a left direction with reference to the drawing, the vent 72 forms a passage through which air is exhausted.
Meanwhile, the case of large amount of vibration and the case of small amount of vibration may occur in the drum washing machine. For example, a large amount of vibration occurs since a change in a drum rotation speed is great during an intermittent dewatering mode, and a small amount of vibration occurs since a change in a drum rotation speed is small during a continuous dewatering mode.
However, the same damping force is always generated in the general damper 8, as described above. Therefore, in case a small amount of vibration occurs, the damper 8 acts as a rigid body, such that an amount of vibration cannot be rapidly attenuated due to a vibration exceeding a displacement limit of the damper 8 and the damper 8 may be damaged. Considering this, it is usual to form the damper 8 to match the case a large amount of vibration occurs.
Since such a conventional damper cannot properly cope with the change in an amount of vibration, noise and vibration occur seriously, thereby causing an inconvenience of use.
In other words, there is a demand for a damper which can apply a large damping force when a large amount of vibration is generated and can apply a small damping force when a small amount of vibration is generated, thereby rapidly reducing the vibration and noise.